1. Field of the Invention
The present invention relates in general to evaporative emission control systems for automotive vehicles and more particularly to a vent system for venting fuel vapor from a fuel tank of an automotive vehicle.
2. Description of the Prior Art
An increase of the pressure in a fuel tank due to vaporization of fuel is disadvantageous since it may adversely affect the supply of fuel to an associated engine, cause deformation of the fuel tank, or otherwise cause harm. In order to prevent this, prior practice has been to vent the fuel tank to an engine induction system by way of a canister so that the vapor in the fuel tank is drawn into the induction system for burning in a combustion chamber.
FIG. 10 shows a prior art fuel tank vent system including a fuel tank 20 having an upper vacant space S therewithin and a separator 21 disposed within the space S. The separator 21 has ports 22, 23 at the bottom wall and an upper part of the lateral wall thereof, respectively, and further has at the top wall thereof a vent pipe 24 projecting outside of the fuel tank 20. The vent pipe 24 is connected with a vent hose 25 in communciation with a canister (not shown) and is so arranged as to be higher in position than the surface of liquid fuel even when the vehicle turns a tight corner very rapidly or inclines greatly, with the fuel tank 20 being completely filled.
With the above arrangement, when the vehicle is on a horizontal road, to allow the surface of fuel in the fuel tank 20 to coincide with the solid line level in the drawing, fuel vapor flows into the separator 21 through the ports 22, 23 and is drawn through the vent pipe 24 outside of the fuel tank 20 and to the canister. When the vehicle inclines maximumly to the right or turns very rapidly to the left, the port 22 sinks under the surface of fuel represented by the one-dot chain line level (f) in the drawing. However, in this case, the port 23 and the inlet of the vent pipe 24 are positioned above the surface (f) of fuel. On the other hand, when the vehicle inclines maximumly to the left or turns very rapidly to the right, both ports 22, 23 sink under the surface of fuel represented by the one-dot chain line level (e) in the drawing. However, in this case, the inlet of the vent pipe 24 is positioned above the surface (e) of fuel. In the above manner, liquid fuel in the fuel tank 20 is prevented from flowing directly into the vent pipe 24. A structure similar to the above is disclosed in the Japanese Provisional Utility Model Publication No. 47-24496.
With the prior art vent system, while flow of liquid fuel directly into the vent pipe 24 can be prevented even when the vehicle inclines maximumly or turns very rapidly, it still can occur that liquid fuel flows out of the fuel tank 20 through the vent pipe 24 when the vehicle is parked for a long time and the ports 22, 23 remain below the surface of fuel, as, for example, when the surface of fuel coincides with the level (e). Under such a condition, the pressure in the fuel tank 20, namely, the pressure in the space S, increases with vaporization of fuel, forcing fuel to flow into the separator 21 and causing the surface of fuel therein to rise until fuel flows into the vent pipe 24. For this reason, it is necessary that separator 21 be as large as possible and be placed above the surface of fuel in the fuel tank 20 even when the fuel tank 20 is maximumly filled, resulting in the problem that such a separator inevitably reduces the effective volume of a fuel tank.